1. Field of the Invention
The present invention relates to a method for measuring electrical potentials, and more particularly to a method for measuring electrical potentials at solid state matter which is separated from a surface by at least one conductive layer and at least one insulating layer wherein ionizing radiation is directed against a measuring point at the surface.
2. Description of the Prior Art
Electrical potentials of solid state matter which are hidden below an insulating layer and a conductive cover layer such as, for example, potentials under the gate electrode of a metal-oxide-semiconductor (MOS) structure or, for example, potentials of a hidden path within a multi-layer wiring are to be measured topically resolved and in a non-destructive manner.
When only an insulating cover layer is located at the surface of a specimen, then, based on the knowledge in this art, a potential measurement at a solid state matter which is hidden beneath the cover layer is possible in a scanning electron microscope with the assistance of a known method of potential contrast when the primary beam energy is sufficiently high as to form a conductive channel in the entire thickness of the insulating cover layer. This known method fails, however, when the insulating layer is, in turn, additionally covered by a conductive cover layer. In order to measure the potential at a solid state substance which is covered under at least one conductive layer and at least one insulating layer, therefore, the layers lying thereabove previously had to be eroded.